import java.util.Scanner;

public class text2 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入圆的半径");
        double r = sc.nextDouble();
        double s = circleArea(r);
        System.out.println("圆的面积为" + s);
    }

    public static double circleArea(double r) {
        return r * r * 3.14;
    }
}
